This proposal is directed toward the study of the phosphoprotein phosphatases. As their name implies, these are enzyme catalysts which remove phosphate groups covalently attached to proteins. The significance of these studies lies in the findings that phosphorylation of proteins at specific sites is a regulatory mechanism in the control of mammalian metabolism. Thus, these proteins exist in two forms, phosphorylated and dephosphorylated forms, which have different activity states. The protein phosphatases are responsible for the interconversion leading to the dephosphorylated state. The specific goals of the proposal are the isolation and characterization of these enzymes from skeletal muscle. They will be studied in reference to the actions on the enzymes of glycogen metabolism. These studies are directed to improving our basic understanding of the complex mechanisms involved in the control of metabolism via covalent modification of proteins.